1. Field of the Invention
The present invention relates to a control method of the motor rotation speed, and more particularly, the present invention relates to a control method of the motor rotation speed used in an optical disc drive.
2. Description of Related Art
As the need for high memory capacity to store the media information increases, the use of the optical disc plays an important role. An issue that remains to be solved by manufacturers is how to read the information on the optical disc at a fast speed and stable quality, so as to reduce the data access time.
Referring to FIG. 1, a block diagram, schematically illustrates the circuit of a conventional control system 100 of the motor rotation speed used in an optical disc drive. In the conventional optical disc drive, the optical disc 102 is disposed on a spindle motor 104. The spindle motor 104 is used to rotate the optical disc 102 according to the control signal of rotation speed (DMO) outputted by a motor control apparatus 106. The spindle motor 104 and a frequency generator (FG) 108 are coupled together, in which the frequency generator 108 will output the frequency signal of rotation speed (SF), according to the rotation speed of the optical disc 102, and feed it back to the motor control apparatus 106. The motor control apparatus 106 includes a microprocessor 108 and a digital signal processor (DSP) 110, and outputs the control signal of rotation speed (DMO) to the spindle motor 104, according to the frequency signal of rotation speed (SF) and a current operation status of the optical disc drive. In this manner, the optical disc drive can achieve the control action of the rotation speed on the optical disc 102 by using the control system 100 of the rotation speed in a type of closed loop.
There are a number of tracks on the optical disc 102 for storing the digital information, in which the digital information is to be read by an optical pickup head. When reading the digital information, the optical pickup head needs to move to a proper position to perform the reading operation, in accordance with the different position of the digital information stored on the optical disc 102. At the same time, the control system 100 of the rotation speed also needs to control the rotation speed of the optical disc 102, according to the position of the digital information stored on the optical disc 102. For example, the rotation speed of the optical disc 102 is faster when reading the digital information stored closer to the center of the optical disc 102. On the contrary, when the digital information has been stored closer to the outer edge of the optical disc 102, the rotation speed of the optical disc 102 is slower.
When the rotation of the optical disc 102 is intended to be ceased, the motor control apparatus 106 will output a control signal of rotation speed (DMO), according to the frequency signal of rotation speed (SF) fed by the frequency generator 108, so as to allow the spindle motor 104 to apply a torque on the optical disc 102 and thereby decrease the rotation speed of the optical disc 102. Wherein, the direction of the torque applied on the optical disc 102 is opposite to the rotation direction of the optical disc 102. When the motor control apparatus 106 has detected a zero rotation speed of the optical disc 102 by the frequency signal of rotation speed (SF) outputted by the frequency generator 108, then the control signal of rotation speed (DMO) stops outputting. For clarity of description, the time period, from when the optical disc 102 is intended to be ceased to when the optical disc 102 is decreased to zero, is called the braking time period herein.
The drawbacks for the conventional control system of the rotation speed are as follows: firstly, it requires a frequency generator to output the feedback signal. Secondly, the design for the conventional control system for the rotation speed in a closed loop would be more complicated and the fabrication cost would be higher.